The behaviour and ecology of the zebrafish, Danio rerio
Though the zebrafish is an important laboratory model organism, little is known about its natural ecology, and few studies have been conducted on wild populations. It is a small, shoaling cyprinid, native to the floodplains of the Indian subcontinent. A survey conducted in Bangladesh showed that it is most abundant in shallow lakes, ponds and ditches, often associated with rice cultivation. Length-frequency analysis indicates that the zebrafish is an annual species, recruitment being linked to the monsoon season. Its diet, based on gut content analysis, consists primarily of zooplankton and insects. Zebrafish are group spawners and egg scatterers, though females are choosy with respect to sites for oviposition and males defend territories around such sites. The reproductive success of both females and males is affected by density; females produce smaller clutches at higher densities; at low densities territorial males achieve greater reproductive success than non-territorial males, but at higher densities they are no more successful than non-territorials. Female mating preferences, when assessed in the absence of male-male competition, do not correspond to male dominance. The opportunity for selection appears to be weak in zebrafish. Zebrafish show innate and learned preferences for visual cues, both in social and foraging contexts. They shoal preferentially with their own colour pattern, but when individuals are cross-reared with groups of an alternative colour pattern, they prefer to shoal with fish of the appearance with which they were reared; there appears to be a strong learned component to species recognition. In a foraging context, zebrafish display both innate and learned colour preferences. When fish were reared on diets consisting of different colours, each group respond most strongly to red, although there was also an effect of conditioning. This project provides a basis for further studies linking adaptive behaviour with gene expression in zebrafish.